Selective germanium p-contact metalization through trench

ABSTRACT

Techniques are disclosed for forming transistor devices having reduced parasitic contact resistance relative to conventional devices. The techniques can be implemented, for example, using a standard contact stack such as a series of metals on, for example, silicon or silicon germanium (SiGe) source/drain regions. In accordance with one example such embodiment, an intermediate boron doped germanium layer is provided between the source/drain and contact metals to significantly reduce contact resistance. Numerous transistor configurations and suitable fabrication processes will be apparent in light of this disclosure, including both planar and non-planar transistor structures (e.g., FinFETs), as well as strained and unstrained channel structures. Graded buffering can be used to reduce misfit dislocation. The techniques are particularly well-suited for implementing p-type devices, but can be used for n-type devices if so desired.

RELATED APPLICATION

This patent application is a continuation of U.S. application Ser. No.15/162,551 filed on May 23, 2016 (now U.S. Pat. No. 9,698,219) which isa continuation of U.S. application Ser. No. 14/807,285 filed on Jul. 23,2015 (now U.S. Pat. No. 9,349,810), which is a continuation of U.S.application Ser. No. 13/990,238 filed May 29, 2013 (now U.S. Pat. No.9,117,791), which is a U.S. National Phase application under 35 U.S.C. §371 of International Application No. PCT/US2011/054202 filed Sep. 30,2011, which is a continuation-in-part of U.S. application Ser. No.12/975,278 filed Dec. 21, 2010 (now U.S. Pat. No. 8,901,537). Each ofthese applications is incorporated herein by reference in its entirety.

BACKGROUND

Increased performance of circuit devices including transistors, diodes,resistors, capacitors, and other passive and active electronic devicesformed on a semiconductor substrate is typically a major factorconsidered during design, manufacture, and operation of those devices.For example, during design and manufacture or forming of, metal oxidesemiconductor (MOS) transistor semiconductor devices, such as those usedin a complementary metal oxide semiconductor (CMOS), it is often desiredto minimize the parasitic resistance associated with contacts otherwiseknown as external resistance R_(ext). Decreased R_(ext) enables highercurrent from an equal transistor design.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a MOS device configured with a boron doped germaniumlayer between the source/drain layer and contact metals, in accordancewith an embodiment of the present invention.

FIG. 1B illustrates a MOS device configured with a boron doped germaniumlayer between the source/drain layer and contact metals, in accordancewith another embodiment of the present invention.

FIG. 1C illustrates a MOS device configured with a boron doped germaniumlayer between the source/drain layer and contact metals, in accordancewith another embodiment of the present invention.

FIG. 2 is a method for forming a transistor structure with low contactresistance in accordance with an embodiment of the present invention.

FIGS. 3A to 3I illustrate structures that are formed when carrying outthe method of FIG. 2, in accordance with various embodiment of thepresent invention.

FIG. 4 is a method for forming a transistor structure with low contactresistance in accordance with another embodiment of the presentinvention.

FIGS. 5A to 5F illustrate structures that are formed when carrying outthe method of FIG. 4, in accordance with various embodiment of thepresent invention.

FIG. 6 shows a perspective view of a FinFET transistor architecture,configured in accordance with one embodiment of the present invention.

FIG. 7 shows a plot of a split lot showing contact resistance fortransistor structures configured with in accordance with embodiments ofthe present invention and standard transistor structures configured withno cap.

FIG. 8 illustrates a computing system implemented with one or moretransistor structures in accordance with an example embodiment of thepresent invention.

As will be appreciated, the figures are not necessarily drawn to scaleor intended to limit the claimed invention to the specificconfigurations shown. For instance, while some figures generallyindicate straight lines, right angles, and smooth surfaces, an actualimplementation of a transistor structure may have less than perfectstraight lines, right angles, and some features may have surfacetopology or otherwise be non-smooth, given real world limitations of theprocessing equipment and techniques used. In short, the figures areprovided merely to show example structures.

DETAILED DESCRIPTION

Techniques are disclosed for forming transistor devices having reducedparasitic contact resistance relative to conventional devices. Thetechniques can be implemented, for example, using a standard contactstack such as a series of metals on silicon or silicon germanium (SiGe)source/drain regions. In accordance with one example such embodiment, anintermediate boron doped germanium layer is provided between thesource/drain and contact metals to significantly reduce contactresistance. Numerous transistor configurations and suitable fabricationprocesses will be apparent in light of this disclosure, including bothplanar and non-planar transistor structures (e.g., FinFETs), as well asstrained and unstrained channel structures. The techniques areparticularly well-suited for implementing p-type devices, but can beused for n-type devices if so desired.

General Overview

As previously explained, increased drive current in the transistors canbe achieved by reducing device resistance. Contact resistance is onecomponent of a device's overall resistance. A standard transistorcontact stack typically includes, for example, a silicon or SiGesource/drain layer, a nickel silicide layer, a titanium nitride adhesionlayer, and a tungsten contact/pad. In such configurations, the contactresistance is effectively limited by the silicon or SiGe valence bandalignment to the pinning level in the metal. Typically, using industrystandard silicides such as nickel (or other suitable silicides, such astitanium, cobalt, or platinum), this results in a band misalignment ofabout 0.5 eV. Thus, and in accordance with an example embodiment of thepresent invention, an intermediate boron doped germanium layer isprovided between the source/drain and contact metals to significantlyreduce the band misalignment value and contact resistance.

In one specific example embodiment, contacts configured with theintermediate boron doped germanium layer exhibit a reduction in the bandmisalignment value to less than 0.2 eV and a corresponding reduction incontact resistance of about 3X (relative to a conventional contact stacksimilarly configured, but without the intermediate boron doped germaniumlayer between the source/drain regions and contact metal). Atransmission electron microscopy (TEM) cross section or secondary ionmass spectrometry (SIMS) profile can be used to show the germaniumconcentration throughout the vertical stack of the film structure, asprofiles of epitaxial alloys of silicon and SiGe can readily bedistinguished from germanium concentration profiles.

Thus, transistor structures configured in accordance with embodiments ofthe present invention provide an improvement over conventionalstructures with respect to lower contact resistance. Some suchembodiments effectively marry superior contact properties of germaniumwith superior semiconductor transistor properties of Si and SiGe toprovide next generation low resistance contacts. Selectivity can beachieved in various ways. In one embodiment, for instance, selectivityto n-type MOS (NMOS) source/drain locations can be provided by havingNMOS regions masked off during p-type MOS device (PMOS) deposition. Inanother embodiment, both NMOS and PMOS regions can be opensimultaneously, but deposition only occurs in the PMOS regions by way ofa trench. An advantage here is that the low melting point germanium isabsent during the relatively high thermal budget steps typical in thefront end of a MOS flow. After trench processing and germaniumdeposition, and in accordance with one specific such example embodiment,the structure sees no temperatures above 500° C., and therefore thegermanium overlayer is not in jeopardy of melting and or otherwisedegrading performance. As will be further appreciated in light of thisdisclosure, selectively may include natural selectivity. For instance,while boron doped germanium grows on p-type SiGe (or silicon) sourcedrain regions, it does not grow on dielectric surfaces such as silicondioxide (SiO₂) or silicon nitride (SiN); nor does it grow on, forinstance, exposed heavily phosphorous doped silicon in n-type regions.

Numerous transistor configurations and suitable fabrication processeswill be apparent in light of this disclosure, including both planar andnon-planar transistor structures (e.g., such as double-gate and trigatetransistor structures), as well as strained and unstrained channelstructures. Any number of such structural features and material systemscan be used in conjunction with a germanium overlayer as describedherein. The transistor structure may include p-type source/drainregions, n-type source/drain regions, or both n-type and p-typesource/drain regions. In some example embodiments, the transistorstructure includes dopant-implanted source/drain regions or epitaxial(or poly) replacement source/drain regions of silicon, SiGe alloys, ornominally pure germanium films (e.g., such as those with less than 10%silicon) in a MOS structure. In any such implementations, an overlayeror cap of boron doped germanium can be formed directly over thesource/drain regions, in accordance with an embodiment of the presentinvention. A contact metal (or series of metals) can then be depositedand a subsequent reaction (annealing) can be carried out to form metalgermanide source and drain contacts. As will be appreciated, the contactmay be implemented as a stack including one or more of a silicide layer,an adhesion layer, and/or a metal pad layer. The boron doped germaniumoverlayer can be formed directly over other parts of the transistorstructure as well, such as the poly gate and/or grounding tap regions,if so desired.

As is known, a MOS transistor may include source and drain tip regionsthat are designed to decrease the overall resistance of the transistorwhile improving short channel effects (SCE). Conventionally, these tipregions are portions of the substrate where a dopant such as boron orcarbon is implanted using an implant and diffusion technique. The sourcetip region is formed in the area between the source region and thechannel region. Likewise, the drain tip region is formed in the areabetween the drain region and the channel region. Some embodiments of thepresent invention are configured with such conventionally formed tipregions. In other example embodiments, fabrication techniques areemployed to extend self-aligned epitaxial tip (SET) transistors toachieve very near to the theoretical limit of uniaxial strain. This canbe accomplished, for instance, by selective epitaxial deposition in thesource and drain regions as well as their corresponding tip regions toform a bilayer construction of boron doped silicon or SiGe (for thesource/drain regions) capped with an overlayer of a boron dopedgermanium layer in the source/drain and respective tip regions. Thegermanium and boron concentrations can vary, but in some exampleembodiments, the germanium concentration is in the range of 20 atomic %to 100 atomic %, and the boron concentration is in the range of 1E20cm⁻³ to 2E21 cm⁻³ (e.g., germanium concentration in excess of 50 atomic% and boron concentration in excess of 2E20 cm⁻³). Note that the borondoped germanium layer may be provided in the tip regions, but in otherembodiments is just provided over the source/drain regions (and not inthe tip regions).

In still other example embodiments, an optional thin buffer with gradedgermanium concentration and/or boron concentration can be used as aninterfacial layer between the underlying substrate with the source/drainlayer (e.g., silicon or SiGe). Likewise, a thin buffer with gradedgermanium concentration and/or boron concentration can be used as aninterfacial layer between the source/drain layer and the boron dopedgermanium cap. In still other embodiments, the boron doped germaniumoverlayer or source/drain layer themselves can have a graded germaniumand/or boron concentration in a similar fashion as to the optionalbuffers. In any such case, since boron diffusion is suppressed ingermanium (the higher the concentration, the greater the relativesuppression), a high concentration of boron can be doped in thegermanium, which in turn results in lower parasitic resistance andwithout degrading tip abruptness. In addition, the contact resistance isreduced from lowering of Schottky-barrier height.

Architecture and Methodology

FIG. 1A illustrates a MOS device 100A formed on a substrate 102 andconfigured with a boron doped germanium layer between the source/drainlayer and contact metals, in accordance with an embodiment of thepresent invention. In particular, boron doped germanium layer 117 isprovided between the source layer 110 and contact metals 125, and borondoped germanium layer 119 is provided between the drain layer 112 andcontact metals 127. The source region 110 and the drain region 112 canbe formed using any number of conventional techniques. In this exampleembodiment, for instance, the source region 110 and the drain region 112are formed by etching the substrate and then epitaxially depositing asilicon or silicon germanium material (e.g., with a germaniumconcentration in the range of, for instance, 10 to 70 atomic %).

A gate stack 122 is formed over a channel region 120 of the transistor100A. As can further be seen, the gate stack 122 includes a gatedielectric layer 106 and a gate electrode 104, and spacers 108 areformed adjacent to the gate stack 122. In some example cases, anddepending on the technology node, the spacers 108 create a distance ofabout 10 to 20 nanometers (nm) between the edges of the gate dielectriclayer 106 and the edges of each of the source and drain regions 110/112.It is within this space that a source tip region 110A and a drain tipregion 112A can be formed. In this example embodiment, the tip regions110A/112A are formed via a typical implantation-diffusion based process,and overlap the spacers 108 and may also overlap or underdiffuse thegate dielectric layer 106 by a distance of, for instance, less than 10nm. In forming the implantation-diffusion based tip regions 110A/112A, adopant such as boron or carbon is implanted into the source region 110and the drain region 112. The transistor 100A is then annealed to causethe dopant to diffuse towards the channel region 120. Angled ionimplantation techniques may also be used to further implant dopants intothose areas between the gate dielectric layer 106 and the source/drainregions 110/112. Such implantation-diffusion-based tip formationprocesses generally do not induce a strain on the channel region.

In any case, and as will be appreciated in light of this disclosure,whether a transistor structure has a strained or unstrained channel, orsource-drain tip regions or no source-drain tip regions, is notparticularly relevant to various embodiments of the present invention,and such embodiments are not intended to be limited to any particularsuch structural features. Rather, any number of transistor structuresand types can benefit from employing a boron doped germanium overlayeras described herein. The techniques provided herein are compatible, forinstance, with conventional dopant implanted silicon, raisedsource/drain, strained SiGe (or other suitable materials), and anydeposited epitaxial tip (sometimes referred to as source-drainextensions) that extend below the gate electrode dielectric or arespaced away from the vertical line defined by the gate electrodedielectric.

The germanium overlayer 117/119 is generally provided after formation ofthe source/drain regions 110/112 and prior to formation of the contacts125/127. The thickness of this overlayer 117/119 can vary from oneembodiment to the next, but in one example embodiment is in the range of50 to 250 Angstroms (Å). The boron concentration of overlayer 117/119can also vary, but in one example embodiment is in the range of 1E20cm⁻³ to 2E21 cm⁻³ (e.g., in excess of 2E20 cm⁻³). The overlayer 117/119can be selectively deposited over the source/drain 110/112 regions(and/or other regions as desired, such as the poly gate or grounding tapregions). Any number of suitable deposition techniques can be used toprovide the overlayer 117/119 (e.g., chemical vapor deposition,molecular beam epitaxy, etc). In accordance with one example embodiment,the contact metals 125 and 127 each comprise a stack including a nickelsilicide layer, a titanium nitride adhesion layer, and a tungstencontact/pad, and although any number of contact metal configurations canbe used as will be appreciated in light of this disclosure. Standarddeposition techniques can be used in providing the contact metals125/127.

FIG. 1B illustrates an example MOS device 100B formed on a substrate 102and configured with a boron doped germanium layer 117/119 between thesource/drain layer 110/112 and contact metals 125/127, in accordancewith another embodiment of the present invention. This exampleconfiguration includes source and drain epitaxial tips (generallyreferred to herein as epi-tips). In more detail, the MOS transistor 100Buses an undercut etch to allow the source region 110 and the drainregion 112 to extend below the spacers 108, and in some cases, below thegate dielectric layer 106. The portions of the source/drain regions110/112 that extend below the spacers 108 (and possibly the gatedielectric layer 106) are generally referred to as the source epi-tip110B and the drain epi-tip 112B, respectively. The source and drainepi-tips 110B/112B replace the implantation/diffusion based tip regions110A/112A described with regard to FIG. 1A. In accordance with oneembodiment, the source/drain regions 110/112 and the source/drainepi-tips 110B/112B can be formed, for example, by etching the substrate102, which includes undercutting the spacers 108 (and possibly the gatedielectric layer 106), and then using selective epitaxial deposition toprovide, for instance, an in situ doped silicon, germanium, or SiGe tofill the source/drain regions 110/112 and the source/drain epi-tips110B/112B, as shown in FIG. 1B. Note the epitaxial fill may be raisedrelative to the surface of substrate 102, as further shown in FIG. 1B,although non-raised configurations can be used as well. The germaniumoverlayer 117/119 and the contact metals 125/127 can be implemented, forinstance, as previously described with respect to FIG. 1A.

FIG. 1C illustrates a MOS device 100C formed on a substrate 102 andconfigured with boron doped germanium layers 117/119 between therespective source/drain layers 110/112 and contact metals 125/127, inaccordance with another embodiment of the present invention. The sourceregion 110 and the drain region 112 in this example embodiment areformed by implanting dopants such as boron into the substrate. The gatestack 122 is formed over a channel region 120 of the transistor 100C andis this example case does not include sidewalls 108. Nor does thisexample transistor structure include an undercut or tip regions like theembodiments shown in FIGS. 1A and 1B. The germanium overlayer 117/119and the contact metals 125/127 can be implemented, for instance, aspreviously described with respect to FIG. 1A.

Numerous other variations and features can be implemented for transistorstructures configured in accordance with an embodiment of the presentinvention. For example, a graded buffer may be used in one or morelocations of the structure. For instance, the substrate 102 can be asilicon substrate, or a silicon film of a silicon on insulator (SOI)substrate, or a multi-layered substrate comprising silicon, silicongermanium, germanium, and/or III-V compound semiconductors. Thus, and byway of example, in an embodiment having a silicon or silicon germaniumsubstrate 102 and an in situ boron doped SiGe fill in the source/drainregions 110/112 and the source/drain epi-tips 110B/112B, a buffer can beprovided between the underlying substrate 102 and the source/drainmaterial. In one such embodiment, the buffer can be a graded boron doped(or intrinsic) silicon germanium layer with the germanium concentrationgraded from a base level compatible with the underlying substrate up to100 atomic % (or near 100 atomic %, such as in excess of 90 atomic % or95 atomic % or 98 atomic %). The boron concentration within this buffercan be either fixed (e.g., at a high level) or graded, for instance,from a base concentration at or otherwise compatible with the underlyingsubstrate up to a desired high concentration (e.g., in excess of 2E20cm⁻³). Note that ‘compatibility’ as used herein does not necessitate anoverlap in concentration levels (for instance, the germaniumconcentration of underlying substrate can be 0 to 20 atomic % andinitial germanium concentration of the buffer can be 30 to 40 atomic %).In addition, as used herein, the term ‘fixed’ with respect to aconcentration level is intended to indicate a relatively constantconcentration level (e.g., the lowest concentration level in the layeris within 10% of the highest concentration level within that layer). Ina more general sense, a fixed concentration level is intended toindicate the lack of an intentionally graded concentration level. Thethickness of the buffer can vary depending on factors such as the rangeof concentrations being buffered, but in some embodiments is in therange of 30 to 120 Å, such as 50 to 100 Å (e.g., 60 Å or 65 Å). As willbe further appreciated in light of this disclosure, such a graded bufferbeneficially lowers the Schottky-barrier height.

Alternatively, rather than using a thin buffer between the substrate 102and the source/drain regions 110/112 and the source/drain epi-tips110B/112B, the source/drain material itself can be graded in a similarfashion. For example, and in accordance with one example embodiment,boron doped SiGe source/drain regions 110/112 and the source/drainepi-tips 110B/112B can be configured with a germanium concentrationgraded from a base level concentration compatible with the underlyingsubstrate (e.g., in the range of 30 to 70 atomic %) up to 100 atomic %.In some such embodiments, the boron concentration within this borondoped germanium layer can range, for example, from a base concentrationat or otherwise compatible with the underlying substrate up to a desiredhigh concentration (e.g., in excess of 2E20 cm⁻³).

In other embodiments, a buffer can be provided between the source/drainmaterial and the boron doped germanium overlayer 117/119. In one suchembodiment, the source/drain material is a boron doped SiGe layer havinga fixed concentration of germanium (e.g., in the range of 30 to 70atomic %) and the buffer can be a thin SiGe layer (e.g., 30 to 120 Å,such as 50 to 100 Å) having a germanium concentration graded from a baselevel concentration compatible with the underlying boron doped SiGelayer up to 100 atomic % (or near 100 atomic %, such as in excess of 90atomic % or 95 atomic % or 98 atomic %). In some such cases, the boronconcentration within this buffer can be fixed at a desired high level orcan range, for example, from a base concentration at or otherwisecompatible with the underlying SiGe layer up to the desired highconcentration (e.g., in excess of 1E20 cm⁻³, 2E20 cm⁻³, or 3E20 cm⁻³).Alternatively, rather than using a buffer between the source/drainmaterial and the boron doped germanium overlayer 117/119, the overlayer117/119 itself can be graded in a similar fashion. For example, and inaccordance with one example embodiment, the boron doped overlayer117/119 can be configured with a germanium concentration graded from abase level concentration compatible with the underlying substrate and/orsource/drain regions (e.g., in the range of 30 to 70 atomic %) up to 100atomic % (or near 100 atomic %). The boron concentration within thisoverlayer 117/119 layer can be fixed at a desired high level or canrange, for example, from a base concentration at or otherwise compatiblewith the underlying substrate and/or source/drain regions up to thedesired high level (e.g., in excess of 2E20 cm⁻³).

Thus, a low contact resistance architecture for numerous transistordevices is provided. The devices may be formed in part using any numberof conventional processes such as, for example, by gate oxide, poly gateelectrode, thin spacer, and an isotropic undercut etch in thesource/drain regions (or an ammonia etch to form faceted fin recess inmonocrystalline substrate, or other suitable etch to form fin recess).In accordance with some embodiments, selective epitaxial deposition canbe used to provide in situ doped silicon or alternatively, a fullystrained silicon germanium layer to form source/drain regions with orwithout tips. Optional buffers may be used as previously explained. Anysuitable high-k replacement metal gate (RMG) process flow can also beused, where a high-k dielectric replaces the conventional gate oxide.Silicidation with, for example, nickel, nickel-platinum, or titaniumwith or without germanium pre-amorphization implants can be used to forma low resistance germanide. The techniques provided herein can beapplied, for example, to benefit any technology nodes (e.g., 90 nm, 65nm, 45 nm, 32 nm, 22 nm, 14 nm, and 10 nm transistors, and lower), andthe claimed invention is not intended to be limited to any particularsuch nodes or range of device geometries. Other advantages will beapparent in light of this disclosure.

FIG. 2 is a method for forming a transistor structure with low contactresistance in accordance with an embodiment of the present invention.FIGS. 3A through 3I illustrate example structures that are formed as themethod is carried out, and in accordance with some embodiments.

As can be seen, the method begins with forming 202 a gate stack on asemiconductor substrate upon which a MOS device, such as a PMOStransistor, may be formed. The semiconductor substrate may beimplemented, for example, with a bulk silicon or a silicon-on-insulatorconfiguration. In other implementations, the semiconductor substrate maybe formed using alternate materials, which may or may not be combinedwith silicon, such as germanium, silicon germanium, indium antimonide,lead telluride, indium arsenide, indium phosphide, gallium arsenide, orgallium antimonide. In a more general sense, any material that may serveas a foundation upon which a semiconductor device may be built can beused in accordance with embodiments of the present invention. The gatestack can be formed as conventionally done or using any suitable customtechniques. In some embodiments of the present invention, the gate stackmay be formed by depositing and then patterning a gate dielectric layerand a gate electrode layer. For instance, in one example case, a gatedielectric layer may be blanket deposited onto the semiconductorsubstrate using conventional deposition processes such as chemical vapordeposition (CVD), atomic layer deposition (ALD), spin-on deposition(SOD), or physical vapor deposition (PVD). Alternate depositiontechniques may be used as well, for instance, the gate dielectric layermay be thermally grown. The gate dielectric material may be formed, forexample, from materials such as silicon dioxide or high-k dielectricmaterials. Examples of high-k gate dielectric materials include, forinstance, hafnium oxide, hafnium silicon oxide, lanthanum oxide,lanthanum aluminum oxide, zirconium oxide, zirconium silicon oxide,tantalum oxide, titanium oxide, barium strontium titanium oxide, bariumtitanium oxide, strontium titanium oxide, yttrium oxide, aluminum oxide,lead scandium tantalum oxide, and lead zinc niobate. In some specificexample embodiments, the high-k gate dielectric layer may be betweenaround 5 Å to around 200 Å thick (e.g., 20 Å to 50 Å). In general, thethickness of the gate dielectric layer should be sufficient toelectrically isolate the gate electrode from the neighboring source anddrain contacts. In further embodiments, additional processing may beperformed on the high-k gate dielectric layer, such as an annealingprocess to improve the quality of the high-k material. Next, a gateelectrode material may be deposited on the gate dielectric layer usingsimilar deposition techniques such as ALD, CVD, or PVD. In some suchspecific embodiments, the gate electrode material is polysilicon or ametal layer, although other suitable gate electrode materials can beused as well. The gate electrode material, which is may be a sacrificialmaterial that is later removed for a replacement metal gate (RMG)process, has a thickness in the range of 50Å to 500 Å (e.g., 100 Å), insome example embodiments. A conventional patterning process may then becarried out to etch away portions of the gate electrode layer and thegate dielectric layer to form the gate stack, as shown in FIG. 3A. Ascan be seen, FIG. 3A illustrates a substrate 300 upon which a gate stackis formed. In this example embodiment, the gate stack includes a gatedielectric layer 302 (which may be high-k gate dielectric material) anda sacrificial gate electrode 304. In one specific example case, the gatestack includes a silicon dioxide gate dielectric layer 302 and apolysilicon gate electrode 304. The gate stack may also include a gatehard mask layer 306 that provides certain benefits or uses duringprocessing, such as protecting the gate electrode 304 from subsequention implantation processes. The hard mask layer 306 may be formed usingtypical hard mask materials, such as such as silicon dioxide, siliconnitride, and/or other conventional dielectric materials. FIG. 3A furtherillustrates spacers 310 formed on either side of the stack. The spacers310 may be formed, for example, using conventional materials such assilicon oxide, silicon nitride, or other suitable spacer materials. Thewidth of the spacers 310 may generally be chosen based on designrequirements for the transistor being formed. In accordance with someembodiments, however, the width of the spacers 310 is not subject todesign constraints imposed by the formation of the source and drainepi-tips, given sufficiently high boron doped germanium content in thesource/drain tip regions, as described herein (boron won't diffuse intochannel).

With further reference to FIG. 2, after the gate stack is formed, themethod continues with defining 204 the source/drain regions of thetransistor structure. As previously explained, the source/drain regionscan be implemented with any number of suitable processes andconfigurations. For example, the source/drain regions may be implanted,etched and epi filled, raised, silicon or SiGe alloy, p-type and/orn-type, and have a planar or fin shaped diffusion region. In the exampleembodiment shown in FIG. 3A, substrate 300 has been etched to providecavities 312/314 as well as respective tip areas 312A/314A whichundercut the gate dielectric 302. FIG. 3B illustrates the substrate 300after cavities 312/314 and tip areas 312A/314A have been filled toprovide the source/drain regions 318/320 and tip regions 318A/320A. Inaccordance with some example embodiments, the source and drain regioncavities 312/314 along with their respective tip areas 312A/314A arefilled with in situ doped silicon or SiGe, thereby forming source region318 (along with epi-tip 318A) and drain region 320 (along with drainepi-tip 320A). Any number of source/drain layer configurations can beused here, with respect to materials (e.g., silicon, SiGe, III-Vmaterials), dopant (e.g., boron in excess of 2E21 cm⁻³, or othersuitable dopant/concentration), and dimension (e.g., thickness ofsource/drain layer may range, for instance, from 50 to 500 nm so as toprovide a flush or raised source/drain region).

As previously explained, some such embodiments may include with a thinbuffer between the source/drain layer and the substrate or thesource/drain and boron doped germanium overlayer. For instance, and ascan further be seen in the example embodiment shown in FIG. 3B, a sourcebuffer 313 and a drain buffer 315 are deposited prior to depositing thesource/drain materials. In some embodiments, the buffers 313 and 315 canbe a graded boron doped silicon germanium layer with the germaniumcomposition graded from a base level concentration compatible with theunderlying substrate 300 material up to 100 atomic % (or near to 100atomic % as previously described). The boron concentration can beappropriately graded as well. Numerous buffer schemes will be apparentin light of this disclosure.

With further reference to FIG. 2, after the source/drain regions aredefined, the method continues with depositing 206 boron doped germaniumon the source/drain regions of the transistor structure. FIG. 3C showsthe boron doped germanium layer 317/319. In some example embodiments,the boron doped germanium layer 317/319, which may be epitaxiallydeposited in one or more layers, has a germanium concentration in excessof 90 atomic %, although other suitable concentration levels can be usedas will be appreciated in light of this disclosure (e.g., in excess of91 atomic %, or 92 atomic %, . . . , or 98 atomic %, or 99 atomic %, ortruly pure germanium). As previously explained, this germaniumconcentration may be fixed or graded so as to increase from a base level(near substrate 300) to a high level (e.g., in excess of 90 atomic %).The boron concentration in some such embodiments can be in excess of1E20 cm⁻³, such as higher than 2E20 cm⁻³ or 2E21 cm⁻³, and may also begraded so as to increase from a base level near substrate 300 to a highlevel (e.g., in excess of 1E20 cm⁻³ or 2E20 cm⁻³ or 3E20 cm⁻³, . . . ,2E21 cm⁻³). In embodiments where the germanium concentration of theunderlying source/drain regions 318/320 is fixed or otherwise relativelylow, a graded buffer may be used to better interface source/drainregions 318/320 with the boron doped germanium layer 317/319, aspreviously explained. The thickness of the boron doped germanium cap317/319 may have a thickness in the range, for example, of 50 to 250 Å,in accordance with some specific example embodiments, althoughalternative embodiments may have other layer thicknesses, as will beapparent in light of this disclosure.

In some embodiments, a CVD process or other suitable depositiontechnique may be used for the depositing 206 or otherwise forming theboron doped germanium layer 317/319. For example, the depositing 206 maybe carried out in a CVD, or rapid thermal CVD (RT-CVD), or low pressureCVD (LP-CVD), or ultra-high vacuum CVD (UHV-CVD), or gas sourcemolecular beam epitaxy (GS-MBE) tool using germanium and boroncontaining precursors such as germane (GeH₄) or digermane (Ge₂H₆) anddiborane (B₂H₆) or boron difluoride (BF₂). In some such embodiments,there may be a carrier gas such as, for instance, hydrogen, nitrogen, ora noble gas (e.g., precursor is diluted at 1-5% concentration of carriergas). There may also be an etchant gas such as, for example,halogen-based gas such as hydrogen chloride (HCl), chlorine (Cl), or,hydrogen bromide (HBr). The basic deposition of germanium and also borondoped germanium is possible over a wide range of conditions usingdeposition temperature in the range, for example, of 300° C. to 800° C.(e.g., 300-500° C.) and reactor pressure, for instance, in the range 1Torr to 760 Torr. Germanium is naturally selective in that it depositson silicon or silicon-germanium alloy, and does not deposit on othermaterials such as silicon dioxide and silicon nitride. Since thisnatural selectivity is not entirely perfect, a small flow of etchant canbe used to increase the selectivity of the deposition, as previouslynoted. Each of the carrier and etchants can have a flow in the range of10 and 300 SCCM (typically, no more than 100 SCCM of flow is required,but some embodiments may require higher flow rates). In one specificexample embodiment, the deposition 206 is carried out using GeH₄ that isdiluted in hydrogen at a 1% concentration and at a flow rate that rangesbetween 100 and 1000 SCCM. For an in situ doping of boron, diluted B₂H₆may be used (e.g., the B₂H₆ may be diluted in H₂ at 3% concentration andat a flow rate that ranges between 100 and 600 SCCM. In some suchspecific example cases, an etching agent of HCl or Cl₂ is added at aflow rate that ranges, for example, between 10 and 100 SCCM, to increasethe selectivity of the deposition.

As will be appreciated in light of this disclosure, the selectivity atwhich the boron doped germanium layer 317/319 is deposited can vary asdesired. In some cases, for instance, the boron doped germanium layer317/319 is deposited only on the source/drain regions 318/320 or aportion of the source/drain regions 318/320 (rather than across theentire structure). Any number of masking/patterning techniques can beused to selectively deposit layer 317/319. Moreover, other embodimentsmay benefit from layer 317/319 covering, for example, poly gate regionsor grounding tap regions. As will further be appreciated in light ofthis disclosure, the combination of high germanium concentration (e.g.,in excess of 90 atomic % and up to pure germanium) and high boronconcentration (e.g., in excess of 2E20 cm⁻³) can be used to realizesignificantly lower contact resistance in the source and drain regions(and other areas where low contact resistance is desirable, such asground tap regions), in accordance with some example embodiments.Further, and as previously explained, since boron diffusion issufficiently suppressed by pure germanium, no adverse SCE degradation isrealized with subsequent thermal anneals despite any high boronconcentration proximate the channel (if applicable). Barrier heightlowering is also enabled from the higher concentration of germanium atthe contact surface. In some example embodiments, a germaniumconcentration in excess of 95 atomic % and up to pure germanium (100atomic %) can be used to achieve such benefits.

With further reference to FIG. 2, after the boron doped germanium layer317/319 is provided, the method continues with depositing 208 adielectric over layer 317/319. FIG. 3D shows dielectric 322 as beingflush with the hard mask 306 of the gate stack, but it need not be. Thedielectric can be configured in a number of ways. In some embodiments,dielectric 322 is implemented with SiO₂ or other low-k dielectricmaterials. In other embodiments, dielectric 322 is implemented with aSiN liner followed by one or more layers of SiO₂, or any combination ofnitride, oxide, oxynitride, carbide, oxycarbide, or other suitabledielectric materials). The dielectric 322, which may be referred to asan interlayer dielectric (ILD), may be planarized as commonly done.Other example dielectric materials include, for instance, carbon dopedoxide (CDO), organic polymers such as perfluorocyclobutane orpolytetrafluoroethylene, fluorosilicate glass (FSG), and organosilicatessuch as silsesquioxane, siloxane, or organosilicate glass. In someexample configurations, the ILD layer may include pores or other voidsto further reduce its dielectric constant.

Next, in some embodiments of the present invention where a replacementmetal gate (RMG) process is used and as best shown in FIG. 3E, themethod may further include removing the gate stack (including the high-kgate dielectric layer 302, the sacrificial gate electrode 304, and thehard mask layer 306) using an etching process as conventionally done. Inalternate implementations, only the sacrificial gate 304 and hard masklayer 306 are removed. FIG. 3E illustrates the trench opening that isformed when the gate stack is etched away, in accordance with one suchembodiment. If the gate dielectric layer is removed, the method maycontinue with depositing a new gate dielectric layer into the trenchopening (designated as 324 in FIG. 3F). Any suitable high-k dielectricmaterials such as those previously described may be used here, such ashafnium oxide. The same deposition processes may also be used.Replacement of the gate dielectric layer may be used, for example, toaddress any damage that may have occurred to the original gatedielectric layer during application of the dry and wet etch processes,and/or to replace a low-k or sacrificial dielectric material with ahigh-k or otherwise desired gate dielectric material. As further shownin FIG. 3F, the method may further continue with depositing the metalgate electrode layer 326 into the trench and over the gate dielectriclayer 324. Conventional metal deposition processes may be used to formthe metal gate electrode layer, such as CVD, ALD, PVD, electrolessplating, or electroplating. The metal gate electrode layer may include,for example, a p-type workfunction metal, such as ruthenium, palladium,platinum, cobalt, nickel, and conductive metal oxides, e.g., rutheniumoxide. In some example configurations, two or more metal gate electrodelayers may be deposited. For instance, a workfunction metal may bedeposited in the gate trench followed by a suitable metal gate electrodefill metal such as aluminum or silver.

With further reference to FIG. 2, after dielectric layer 322 is providedover layer 317/319 (and any desired RMG process), the method continueswith etching 210 to form the source/drain contact trenches. Any suitabledry and/or wet etch processes can be used. FIG. 3G shows thesource/drain contact trenches after etching is complete, in accordancewith one example embodiment. The method then continues with depositing212 contact resistance reducing metal and annealing to formsilicide/germanide, and then depositing 214 the source/drain contactplugs. FIG. 3H shows the contact metals 325/327, which in someembodiments includes the silicide/germanide, although other embodimentsmay include additional layers (e.g., adhesion layer). FIG. 31 shows thecontact plug metal 329/331, which in some embodiments includes aluminum,although any suitably conductive contact metal or alloy can be used forthe contact plug 329/331, such as silver, nickel-platinum ornickel-aluminum or other alloys of nickel and aluminum, or titanium,using conventional deposition processes. The germanide/metalization 212of the source and drain contacts can be carried out, for instance, bysilicidation with nickel, aluminum, nickel-platinum or nickel-aluminumor other alloys of nickel and aluminum, or titanium with or withoutgermanium pre-amorphization implants to form a low resistance germanide.The boron doped germanium layer 317/319 allows for metal-germanideformation (e.g., nickel-germanium). The germanide allows forsignificantly lower Schottky-barrier height and improved contactresistance (including R_(ext)) over that in conventional metal-silicidesystems. For instance, conventional transistors typically use asource/drain SiGe epi process, with germanium concentration in the rangeof 30-40 atomic %. Such conventional systems exhibit R_(ext) values ofabout 140 Ohm*um, limited by epi/silicide interfacial resistance, whichis high and may impede future gate pitch scaling. Some embodiments ofthe present invention allow for a significant improvement in R_(ext) inPMOS devices (e.g., about a 2× improvement or better, such as a R_(ext)of about 70 Ohm*um), which can better support PMOS device scaling. Thus,transistors having a source/drain configured with boron doped germaniumcap 317/319 in accordance with an embodiment of the present, with aboron concentration in excess of 1E20 cm⁻³ and a germanium concentrationin excess of 90 atomic % and up to or otherwise near pure germanium (100atomic %) at the interface between the source/drain regions 318/320 andthe contact metals 325/327, can exhibit R_(ext) values of less than 100Ohm*um, and in some cases less than 90 Ohm*um, and in some cases lessthan 80 Ohm*um, and in some cases less than 75 Ohm*um, or lower.

FIG. 4 is a method for forming a transistor structure with low contactresistance in accordance with another embodiment of the presentinvention. FIGS. 5A through 5F illustrate example structures that areformed as the method is carried out, and in accordance with someembodiments. As can be seen, this example transistor structure includesboth p-type and n-type source and drain regions (designated p-S/D andn-S/D, respectively), and the boron doped germanium is selectivelydeposited on the p-type regions only. In general, this method is similarto the method described with reference to FIGS. 2 and 3A-H, except thatthe deposition of the boron doped germanium layer 317/319 on thesource/drain regions is selectively carried out after the dielectric 322is deposited and etched to form the contact trench.

The method includes forming 402 the gate stacks and defining 404 thevarious p-S/D and n-S/D regions using standard processing and as bestshown in FIG. 5A. In some embodiments, the p-S/D and n-S/D regions canbe doped to provide a desired degree of selectivity with respect toboron doped germanium. The method further includes depositing 406 thedielectric 322 directly over the p-S/D and n-S/D regions, as shown inFIG. 5B. The method continues with etching 408 to form the p-S/D andn-S/D region contact trenches, and then selectively depositing 410 theboron doped germanium layer 317/319 into the trench and onto the p-S/Dregions (of which there may be one or more depending on the desiredfunction and application of the transistor structure), as best shown inFIGS. 5C and 5D. Depositing 410 can be carried out using any suitabledeposition process, such as selective epitaxy. Once layer 317/319 isprovided, the method continues with depositing 412 contact metals325/327 on top of the layer 317/319 as well as on top of any exposedn-S/D regions, and then depositing 414 the source/drain contact plugs329/331, as shown in FIGS. 5E and 5F. This alternate methodologyprovides the same benefit of improved contact resistance, but is moreselective in where the boron doped germanium is deposited. Other suchselective deposition processes will be apparent in light of thisdisclosure, using any suitable combination of masking/patterning andselective deposition techniques. As will be further appreciated, theprevious relevant discussion with respect to similar parts of the methodis equally applicable here.

FinFET Configuration

As is known, FinFET is a transistor built around a thin strip ofsemiconductor material (generally referred to as the fin). Thetransistor includes the standard field effect transistor (FET) nodes,including a gate, a gate dielectric, a source region, and a drainregion. The conductive channel of the device resides on the outer sidesof the fin beneath the gate dielectric. Specifically, current runs alongboth sidewalls of the fin (sides perpendicular to the substrate surface)as well as along the top of the fin (side parallel to the substratesurface). Because the conductive channel of such configurationsessentially resides along the three different outer, planar regions ofthe fin, such a FinFET design is sometimes referred to as a tri-gateFinFET. Other types of FinFET configurations are also available, such asso-called double-gate FinFETs, in which the conductive channelprincipally resides only along the two sidewalls of the fin (and notalong the top of the fin).

FIG. 6 shows a perspective view of an example tri-gate architecture,configured in accordance with one embodiment of the present invention.As can be seen, the tri-gate device includes a substrate 600 having asemiconductor body or fin 660 (represented by dashed lines) extendingfrom the substrate 600 through isolation regions 610, 620. A gateelectrode 640 is formed over 3 surfaces of the fin 660 to form 3 gates.A hard mask 690 is formed on top of the gate electrode 640. Gate spacers670, 680 are formed at opposite sidewalls of the gate electrode 640.

A source region comprises the epitaxial region 631 formed on a recessedsource interface 650 and on one fin 660 sidewall, and a drain regioncomprises the epitaxial region 631 formed on a recessed source interface650 and on the opposing fin 660 sidewall (not shown). A cap layer 641 isdeposited over the epitaxial regions 631. Note that the boron cap layer641 may be provided in the recessed (tip) regions, but in otherembodiments is just provided over the source/drain regions (and not inthe recessed regions). In one embodiment, the isolation regions 610, 620are shallow trench isolation (STI) regions formed using conventionaltechniques, such as etching the substrate 600 to form trenches, and thendepositing oxide material onto the trenches to form the STI regions. Theisolation regions 610, 620 can be made from any suitabledielectric/insulative material, such as SiO₂. The previous discussionwith respect to the substrate 102 is equally applicable here (e.g.,substrate 600 may be a silicon substrate, or SOI substrate, or amulti-layered substrate).

As will be appreciated in light of this disclosure, conventionalprocesses and forming techniques can be used to fabricate the FinFETtransistor structure. However, and in accordance with one exampleembodiment of the present invention, the bilayer structure of theepitaxial region 631 and cap layer 641 can be implemented, for instance,using an in situ doped silicon or SiGe (for 631) capped with a borondoped germanium (for 641), with an optional germanium and/or borongraded buffer between the two bilayers. As previously explained, such abuffer may be used to transition from a base level germanium/boronconcentration compatible with the epitaxial region 631 to the borondoped germanium cap 641. Alternatively, germanium and/or boronconcentration grading can be implemented directly in the epitaxialregion 631 and/or the cap 641, rather than in an intervening gradedbuffer arrangement. As will further be appreciated, note that analternative to the tri-gate configuration is a double-gate architecture,which includes a dielectric/isolation layer on top of the fin 660.

FIG. 7 shows a plot of a split lot showing contact resistance fortransistor structures configured with in accordance with embodiments ofthe present invention and standard transistor structures configured withno cap. The transistor structures associated with the high resistancenumbers in excess of 0.18 are all implemented with standard SiGe alloyraised PMOS source/drain regions with contact metal deposited directlythereon. The transistor structures associated with the resistancenumbers of 0.107 and lower are all similarly implemented but with theaddition a boron doped germanium cap between the source/drain regionsand contact metal, in accordance with various embodiments of the presentinvention. Table 1 shows the raw data quantiles resulting from testingof the example structures with and without a boron doped germanium capas described herein.

TABLE 1 Ge Cap Min 10% 25% Median 75% 90% Max Yes 0.032 0.032 0.0330.040 0.078 0.105 0.107 No 0.183 0.183 0.192 0.239 0.250 0.265 0.265As can be seen, this example lot actually shows an improvement(reduction) in contact resistance of about a three to six times (3× to6× ) over conventional transistor structures. The units are Ohms perarbitrary area.

Other improvements enabled by using a boron doped germanium cap inaccordance with an embodiment of the present invention will be apparentin light of this disclosure. In particular, the resulting germanidematerials and Schottky barrier height improvement enables more than a 2×R_(ext) improvement over that in conventional SiGe source/drain PMOSdevices, in accordance with some example embodiments of the presentinvention. As is known, the Schottky barrier height is the barrier forelectrical conduction across a semiconductor-metal junction. Themagnitude of the Schottky barrier height reflects a mismatch in theenergy position of the metal's Fermi level and the majority carrier bandedge of the semiconductor across the semiconductor-metal interface. Fora p-type semiconductor-metal interface, the Schottky barrier height isthe difference between the metal Fermi level and the valence bandmaximum of the semi conductor.

Example System

FIG. 8 illustrates a computing device 1000 configured in accordance withone embodiment of the invention. As can be seen, the computing device1000 houses a motherboard 1002. The motherboard 1002 may include anumber of components, including but not limited to a processor 1004 andat least one communication chip 1006, each of which can be physicallyand electrically coupled to the motherboard 1002, or otherwiseintegrated therein. As will be appreciated, the motherboard 1002 may be,for example, any printed circuit board, whether a main board or adaughterboard mounted on a main board or the only board of device 1000,etc. Depending on its applications, computing device 1000 may includeone or more other components that may or may not be physically andelectrically coupled to the motherboard 1002. These other components mayinclude, but are not limited to, volatile memory (e.g., DRAM),non-volatile memory (e.g., ROM), a graphics processor, a digital signalprocessor, a crypto processor, a chipset, an antenna, a display, atouchscreen display, a touchscreen controller, a battery, an audiocodec, a video codec, a power amplifier, a global positioning system(GPS) device, a compass, an accelerometer, a gyroscope, a speaker, acamera, and a mass storage device (such as hard disk drive, compact disk(CD), digital versatile disk (DVD), and so forth). Any of the componentsincluded in computing device 1000 may include one or more transistorstructures as described herein. In some embodiments, multiple functionscan be integrated into one or more chips (e.g., for instance, note thatthe communication chip 1006 can be part of or otherwise integrated intothe processor 1004).

The communication chip 1006 enables wireless communications for thetransfer of data to and from the computing device 1000. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chip 1006 may implementany of a number of wireless standards or protocols, including but notlimited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE,GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well asany other wireless protocols that are designated as 3G, 4G, 5G, andbeyond. The computing device 1000 may include a plurality ofcommunication chips 1006. For instance, a first communication chip 1006may be dedicated to shorter range wireless communications such as Wi-Fiand Bluetooth and a second communication chip 1006 may be dedicated tolonger range wireless communications such as GPS, EDGE, GPRS, CDMA,WiMAX, LTE, Ev-DO, and others.

The processor 1004 of the computing device 1000 includes an integratedcircuit die packaged within the processor 1004. In some embodiments ofthe present invention, the integrated circuit die of the processorincludes an onboard non-volatile memory or cache, and/or is otherwisecommunicatively coupled to off-chip memory that is implemented with oneor more transistor structures as described herein. The term “processor”may refer to any device or portion of a device that processes, forinstance, electronic data from registers and/or memory to transform thatelectronic data into other electronic data that may be stored inregisters and/or memory.

The communication chip 1006 may also include an integrated circuit diepackaged within the communication chip 1006. In accordance with somesuch example embodiments, the integrated circuit die of thecommunication chip includes one or more devices implemented with one ormore transistor structures as described herein. As will be appreciatedin light of this disclosure, note that multi-standard wirelesscapability may be integrated directly into the processor 1004 (e.g.,where functionality of any chips 1006 is integrated into processor 1004,rather than having separate communication chips). Further note thatprocessor 1004 may be a chip set having such wireless capability. Inshort, any number of processor 1004 and/or communication chips 1006 canbe used. Likewise, any one chip or chip set can have multiple functionsintegrated therein.

In various implementations, the computing device 1000 may be a laptop, anetbook, a notebook, a smartphone, a tablet, a personal digitalassistant (PDA), an ultra-mobile PC, a mobile phone, a desktop computer,a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player,or a digital video recorder. In further implementations, the device 1000may be any other electronic device that processes data or employstransistors.

Numerous embodiments will be apparent in light of this disclosure, andfeatures described herein can be combined in any number ofconfigurations. One example embodiment of the present invention providesa transistor device. The device includes a substrate having a channelregion, and a gate electrode above the channel region. A gate dielectriclayer is provided between the gate electrode and the channel region, andp-type and n-type source/drain regions are provided in the substrate andadjacent to the channel region. The device further includes a borondoped germanium layer on at least a portion of the p-type source/drainregion. This boron doped germanium layer comprises a germaniumconcentration in excess of 90 atomic % and a boron concentration inexcess of 1E20 cm⁻³. The device further includes a metal-germanidesource/drain contact on the boron doped germanium layer. In one suchexample, the boron doped germanium layer is only on p-type source/drainregions of the device. In another example case, the device furtherincludes an interlayer dielectric. In another example case, the devicefurther includes a graded buffer between the substrate and at least oneof the p-type and n-type source/drain regions, and/or a graded bufferbetween at least one of the p-type and n-type source/drain regions andthe boron doped germanium layer. In one such case, the graded bufferbetween the at least one p-type and n-type source and drain regions andthe boron doped germanium layer has a germanium concentration that isgraded from a base level concentration compatible with the at least oneof the p-type and n-type source/drain regions to a high concentration inexcess of 95 atomic %. In one such specific example case, the highconcentration reflects pure germanium. In another example case, thegraded buffer between the at least one of the p-type and n-typesource/drain regions and the boron doped germanium layer has a boronconcentration that is graded from a base level concentration compatiblewith the at least one of the p-type and n-type source/drain regions to ahigh concentration in excess of 1E20 cm⁻³. In another example case, theboron doped germanium layer has a graded concentration of at least oneof germanium and boron. In another example case, the p-type and n-typesource/drain regions comprise silicon germanium having a germaniumconcentration that is graded from a base level concentration compatiblewith the substrate to a high concentration in excess of 50 atomic %, andthe boron doped germanium layer has a germanium concentration in excessof 95 atomic %. In another example case, the p-type and n-typesource/drain regions comprise boron doped silicon germanium having aboron concentration that is graded from a base level concentrationcompatible with the substrate to a high concentration in excess of 1E20cm⁻³. In another example case, the p-type and n-type source/drainregions comprise silicon or silicon germanium, and the device furthercomprises a buffer between at least one of the p-type and n-typesource/drain regions and the boron doped germanium layer, the bufferhaving a germanium concentration that is graded from a base levelconcentration compatible with the at least one of the p-type and n-typesource/drain regions to a high concentration in excess of 50 atomic %,and a boron concentration that is graded from a base level concentrationcompatible with the at least one of the p-type and n-type source/drainregions to a high concentration in excess of 1E20 cm⁻³. In anotherexample case, the boron doped germanium layer comprises a germaniumconcentration in excess of 98 atomic %, and a boron concentration inexcess of 2E20 cm⁻³. Another embodiment provides an electronic devicethat includes a printed circuit board having one or more integratedcircuits, wherein at least one of the one or more integrated circuitscomprises one or more transistor devices as variously defined in thisparagraph. In one such case, the one or more integrated circuitsincludes at least one of a communication chip and/or a processor, and atleast one of the communication chip and/or processor comprises the oneor more transistor devices. In another such case, the device is acomputing device (e.g., mobile telephone or smartphone, laptop, tabletcomputer, etc).

Another embodiment of the present invention provides a transistordevice. In this example case, the device includes a substrate having achannel region, and a gate electrode above the channel region, wherein agate dielectric layer is provided between the gate electrode and thechannel region and spacers are provided on sides of the gate electrode.The device further includes p-type and n-type source/drain regions inthe substrate and adjacent to the channel region, each of the p-type andn-type source/drain regions including a tip region that extends underthe gate dielectric layer and/or a corresponding one of the spacers. Thedevice further includes a boron doped germanium layer on at least aportion of the p-type source/drain region, and comprising a germaniumconcentration in excess of 95 atomic % and a boron concentration inexcess of 2E20 cm⁻³. The device further includes metal-germanidesource/drain contacts on the boron doped germanium layer. The device isone of a planar or FinFET transistor. In one such example case, thedevice further includes a buffer between at least one of the p-type andn-type source/drain regions and the boron doped germanium layer, whereinthe buffer has a germanium concentration that is graded from a baselevel concentration compatible with the at least one of the p-type andn-type source/drain regions to a high concentration in excess of 95atomic %, and a boron concentration that is graded from a base levelconcentration compatible with the at least one of the p-type and n-typesource/drain regions to a high concentration in excess of 2E20 cm⁻³. Inanother example case, the boron doped germanium layer has a gradedconcentration of at least one of germanium and boron. In another examplecase, the p-type and n-type source/drain regions comprise silicongermanium having a germanium concentration that is graded from a baselevel concentration compatible with the substrate to a highconcentration in excess of 50 atomic %, and the boron doped germaniumlayer has a germanium concentration in excess of 98 atomic %. In anotherexample case, the p-type and n-type source/drain regions have a boronconcentration that is graded from a base level concentration compatiblewith the substrate to a high concentration in excess of 2E20 cm⁻³. Inanother example case, the p-type and n-type source/drain regionscomprise silicon germanium having a fixed germanium concentration, andthe device further comprises a buffer between the p-type and n-typesource/drain regions and the boron doped germanium layer, the bufferhaving a germanium concentration that is graded from a base levelconcentration compatible with the p-type and n-type source/drain regionsto a high concentration in excess of 50 atomic %, and a boronconcentration that is graded from a base level concentration compatiblewith the p-type and n-type source/drain regions to a high concentrationin excess of 2E20 cm⁻³, the buffer having a thickness of less than 100Angstroms. Another embodiment provides a computing device (e.g., desktopor portable computer, etc) that includes a printed circuit board havinga communication chip and/or a processor, wherein at least one of thecommunication chip and/or processor comprises one or more transistordevices as variously defined in this paragraph.

Another embodiment of the present invention provides a method forforming a transistor device. The method includes providing a substratehaving a channel region, and providing a gate electrode above thechannel region, wherein a gate dielectric layer is provided between thegate electrode and the channel region. The method continues withproviding p-type and n-type source/drain regions in the substrate andadjacent to the channel region, and providing a boron doped germaniumlayer on at least a portion of the p-type source/drain region. The borondoped germanium layer comprises a germanium concentration in excess of90 atomic % and a boron concentration in excess of 1E20 cm⁻³. The methodcontinues with providing metal-germanide source/drain contacts on theboron doped germanium layer. In some example such cases, the methodfurther includes providing a graded buffer between the substrate and atleast one of the p-type and n-type source/drain regions, and/orproviding a graded buffer between at least one of the p-type and n-typesource/drain regions and the boron doped germanium layer. In anotherexample case, the boron doped germanium layer has a graded concentrationof at least one of germanium and boron (which may be used with orwithout graded buffers). This method may be employed, for example, inthe fabrication of any electronic devices such as a computing device.

The following examples pertain to further embodiments, from whichnumerous permutations and configurations will be apparent.

Example 1 is a transistor device, comprising: a substrate having achannel region; a gate electrode above the channel region, wherein agate dielectric layer is provided between the gate electrode and thechannel region; p-type and n-type source/drain regions in the substrateand adjacent to the channel region; a boron doped germanium layer on atleast a portion of the p-type source/drain region, and comprising agermanium concentration in excess of 90 atomic % and a boronconcentration in excess of 1E20 cm⁻³; and a metal-germanide source/draincontact on the boron doped germanium layer.

Example 2 includes the subject matter of Example 1, wherein the deviceis one of a planar or FinFET transistor.

Example 3 includes the subject matter of any of Examples 1-2, whereinthe boron doped germanium layer is only on p-type source/drain regionsof the device.

Example 4 includes the subject matter of any of Examples 1-3, furthercomprising an interlayer dielectric.

Example 5 includes the subject matter of any of Examples 1-4, furthercomprising at least one of: a graded buffer between the substrate and atleast one of the p-type and n-type source/drain regions; and a gradedbuffer between at least one of the p-type and n-type source/drainregions and the boron doped germanium layer.

Example 6 includes the subject matter of Example 5, wherein the gradedbuffer between at least one of the p-type and n-type source/drainregions and the boron doped germanium layer has a germaniumconcentration that is graded from a base level concentration compatiblewith the at least one of the p-type and n-type source/drain regions to ahigh concentration in excess of 95 atomic %.

Example 7 includes the subject matter of Example 6, wherein the highconcentration reflects pure germanium.

Example 8 includes the subject matter of any of Examples 5-7, whereinthe graded buffer between the at least one of the p-type and n-typesource/drain regions and the boron doped germanium layer has a boronconcentration that is graded from a base level concentration compatiblewith the at least one of the p-type and n-type source/drain regions to ahigh concentration in excess of 1E20 cm⁻³.

Example 9 includes the subject matter of any of Examples 1-8, whereinthe boron doped germanium layer has a graded concentration of at leastone of germanium and boron.

Example 10 includes the subject matter of any of Examples 1-9, whereinthe p-type and n-type source/drain regions comprise silicon germaniumhaving a germanium concentration that is graded from a base levelconcentration compatible with the substrate to a high concentration inexcess of 50 atomic %, and the boron doped germanium layer has agermanium concentration in excess of 95 atomic %.

Example 11 includes the subject matter of any of Examples 1-10, whereinthe p-type and n-type source/drain regions comprise boron doped silicongermanium having a boron concentration that is graded from a base levelconcentration compatible with the substrate to a high concentration inexcess of 1E20 cm⁻³.

Example 12 includes the subject matter of any of Examples 1-4, whereinthe p-type and n-type source/drain regions comprise silicon or silicongermanium, and the device further comprises a buffer between at leastone of the p-type and n-type source/drain regions and the boron dopedgermanium layer, the buffer having a germanium concentration that isgraded from a base level concentration compatible with the at least onep-type and n-type source/drain regions to a high concentration in excessof 50 atomic %, and a boron concentration that is graded from a baselevel concentration compatible with the at least one of the p-type andn-type source/drain regions to a high concentration in excess of 1E20cm⁻³.

Example 13 includes the subject matter of any of Examples 1-12, whereinthe boron doped germanium layer comprises a germanium concentration inexcess of 98 atomic %, and a boron concentration in excess of 2E20 cm⁻³.

Example 14 is an electronic device comprising: a printed circuit boardhaving one or more integrated circuits, wherein at least one of the oneor more integrated circuits comprises one or more transistor devices asdefined in any of the preceding claims.

Example 15 includes the subject matter of Example 14, wherein the one ormore integrated circuits includes at least one of a communication chipand/or a processor, and at least one of the communication chip and/orprocessor comprises the one or more transistor devices.

Example 16 includes the subject matter of Examples 14-15, wherein thedevice is a computing device.

Example 17 is a transistor device, comprising: a substrate having achannel region; a gate electrode above the channel region, wherein agate dielectric layer is provided between the gate electrode and thechannel region and spacers are provided on sides of the gate electrode;p-type and n-type source/drain regions in the substrate and adjacent tothe channel region, each of the p-type and n-type source/drain regionsincluding a tip region that extends under the gate dielectric layerand/or a corresponding one of the spacers; a boron doped germanium layeron at least a portion of the p-type source/drain region, and comprisinga germanium concentration in excess of 95 atomic % and a boronconcentration in excess of 2E20 cm⁻³; and a metal-germanide source/draincontact on the boron doped germanium layer; wherein the device is one ofa planar or FinFET transistor.

Example 18 includes the subject matter of Example 17, furthercomprising: a buffer between at least one of the p-type and n-typesource/drain regions and the boron doped germanium layer, wherein thebuffer has a germanium concentration that is graded from a base levelconcentration compatible with the at least one of the p-type and n-typesource/drain regions to a high concentration in excess of 95 atomic %,and a boron concentration that is graded from a base level concentrationcompatible with the at least one of the p-type and n-type source/drainregions to a high concentration in excess of 2E20 cm⁻³.

Example 19 includes the subject matter of Example 17, wherein the borondoped germanium layer has a graded concentration of at least one ofgermanium and boron.

Example 20 includes the subject matter of Example 17, wherein the p-typeand n-type source/drain regions comprise silicon germanium having agermanium concentration that is graded from a base level concentrationcompatible with the substrate to a high concentration in excess of 50atomic %, and the boron doped germanium layer has a germaniumconcentration in excess of 98 atomic %.

Example 21 includes the subject matter of Example 20, wherein the p-typeand n-type source/drain regions have a boron concentration that isgraded from a base level concentration compatible with the substrate toa high concentration in excess of 2E20 cm⁻³.

Example 22 includes the subject matter of Example 17, wherein the p-typeand n-type source/drain regions comprise silicon germanium having afixed germanium concentration, and the device further comprises a bufferbetween the p-type and n-type source/drain regions and the boron dopedgermanium layer, the buffer having a germanium concentration that isgraded from a base level concentration compatible with the p-type andn-type source/drain regions to a high concentration in excess of 50atomic %, and a boron concentration that is graded from a base levelconcentration compatible with the p-type and n-type source/drain regionsto a high concentration in excess of 2E20 cm⁻³, the buffer having athickness of less than 100 Angstroms.

Example 23 is a method for forming a transistor device, comprising:providing a substrate having a channel region; providing a gateelectrode above the channel region, wherein a gate dielectric layer isprovided between the gate electrode and the channel region; andproviding p-type and n-type source/drain regions in the substrate andadjacent to the channel region; providing a boron doped germanium layeron at least a portion of the p-type source/drain region, the boron dopedgermanium layer comprising a germanium concentration in excess of 90atomic % and a boron concentration in excess of 1E20 cm⁻³; and providingmetal-germanide source/drain contacts on the boron doped germaniumlayer.

The foregoing description of example embodiments of the invention hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseforms disclosed. Many modifications and variations are possible in lightof this disclosure. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto.

What is claimed is:
 1. A semiconductor device, comprising: asemiconductor fin; a gate structure adjacent to a top and opposing sidesof the semiconductor fin, the gate structure including a gate dielectricand a gate electrode, the gate dielectric between the gate electrode andat least a portion of the semiconductor fin; a source region and a drainregion, the source region and the drain region each comprising silicon,germanium, and a p-type dopant, the source region and the drain regioneach having an overall thickness that includes a first graded portion, asecond graded portion, and a substantially fixed portion between thefirst and second graded portions, wherein at least one of the firstgraded portions has a germanium concentration that is graded from a baselevel concentration to a first level concentration, and at least one ofthe second graded portions has a germanium concentration that is gradedfrom the first level concentration to a second level that is in excessof 50 atomic %, the first level being higher than the base level, andthe second level being higher than the first level; and first and secondcontact structures on the source region and the drain region,respectively, the first and second contact structures each includingtitanium, nitrogen, and tungsten.
 2. The semiconductor device of claim1, wherein the base level concentration of germanium is about 0 atomic%, and the first level concentration of germanium is about 30 atomic %.3. The semiconductor device of claim 1, wherein the first and secondcontact structures each include a layer of titanium on the correspondingsource or drain region, a layer of titanium nitride on the layer oftitanium, and a layer of tungsten on the layer of titanium nitride. 4.The semiconductor device of claim 1, wherein the overall thickness ofthe source region is the distance between a bottom of the first contactstructure and a bottom of the source region, and is in the range of 50to 250 nm, and the second graded portion of the source region has athickness in the range of 3 to 12 nm.
 5. The semiconductor device ofclaim 4, wherein the second graded portion of the source region has athickness in the range of 5 to 10 nm.
 6. The semiconductor device ofclaim 1, wherein the overall thickness of the drain region is thedistance between a bottom of the second contact structure and a bottomof the drain region, and is in the range of 50 to 250 nm, and the secondgraded portion of the drain region has a thickness in the range of 3 to12 nm.
 7. The semiconductor device of claim 6, wherein the second gradedportion of the drain region has a thickness in the range of 5 to 10 nm.8. The semiconductor device of claim 1, further comprising: first andsecond recesses in the semiconductor fin, wherein the source region isat least partially in the first recess and the drain region is at leastpartially in the second recess.
 9. The semiconductor device of claim 8,further comprising first and second gate spacers arranged in opposingfashion so that at least part of the gate electrode is between the firstand second gate spacers, wherein one or more of the first and secondrecesses extends under a corresponding one of the first and second gatespacers.
 10. The semiconductor device of claim 1, wherein at least oneof the substantially fixed portions has a lowest concentration level ofgermanium that is within 20% of a highest concentration level ofgermanium in that fixed portion.
 11. The semiconductor device of claim1, wherein at least one of the substantially fixed portions has a lowestconcentration level of germanium that is within 10% of a highestconcentration level of germanium in that fixed portion.
 12. Asemiconductor device, comprising: a semiconductor fin; a gate structureadjacent to a top and opposing sides of the semiconductor fin, the gatestructure including a gate dielectric and a gate electrode, the gatedielectric between the gate electrode and at least a portion of thesemiconductor fin; a source structure and a drain structure, the sourcestructure and the drain structure each comprising silicon, germanium,and a p-type dopant, the source structure and the drain structure eachhaving an overall thickness that includes a first graded portion, asecond graded portion, and a substantially fixed portion between thefirst and second graded portions, wherein at least one of the firstgraded portions has a germanium concentration that is graded from a baselevel concentration to a first level concentration, and at least one ofthe second graded portions has a germanium concentration that is gradedfrom the first level concentration to a second level, the first levelbeing higher than the base level, and the second level being higher thanthe first level; and first and second contact structures on the sourcestructure and the drain structure, respectively, the first and secondcontact structures each including a layer of titanium on thecorresponding source or drain structure, a layer of titanium nitride onthe layer of titanium, and a layer of tungsten on the layer of titaniumnitride; wherein the overall thickness of the source structure is thedistance between a bottom of the first contact structure and a bottom ofthe source structure, and is in the range of 50 to 250 nm, and thesecond graded portion of the source structure has a thickness in therange of 3 to 12 nm; and wherein the overall thickness of the drainstructure is the distance between a bottom of the second contactstructure and a bottom of the drain structure, and is in the range of 50to 250 nm, and the second graded portion of the drain structure has athickness in the range of 3 to 12 nm.
 13. The semiconductor device ofclaim 12, wherein the base level concentration of germanium is about 0atomic %, and the first level concentration of germanium is about 30atomic %.
 14. The semiconductor device of claim 12, wherein the secondlevel is in excess of 50 atomic %.
 15. The semiconductor device of claim12, wherein the second graded portion of the source structure has athickness in the range of 5 to 10 nm.
 16. The semiconductor device ofclaim 12, wherein the second graded portion of the drain structure has athickness in the range of 5 to 10 nm.
 17. The semiconductor device ofclaim 12, further comprising: first and second recesses in thesemiconductor fin, wherein the source structure is at least partially inthe first recess and the drain structure is at least partially in thesecond recess.
 18. The semiconductor device of claim 17, furthercomprising first and second gate spacers arranged in opposing fashion sothat at least part of the gate electrode is between the first and secondgate spacers, wherein one or more of the first and second recessesextends under a corresponding one of the first and second gate spacers.19. The semiconductor device of claim 12, wherein at least one of thesubstantially fixed portions has a lowest concentration level ofgermanium that is within 20% of a highest concentration level ofgermanium in that fixed portion.
 20. The semiconductor device of claim12, wherein at least one of the substantially fixed portions has alowest concentration level of germanium that is within 10% of a highestconcentration level of germanium in that fixed portion.